classgraph-plugin-flag.sh: offer every store-registered version

classgraph-plugin-flag.sh: offer every store-registered version

The store can register several classgraph versions in one db (e.g.
0.2.0.0 alongside 0.2.1.0). The discovery code took only `head -1` of
ghc-pkg's id/library-dirs output, locking onto whichever version sorted
first and reconstructing its .so name — which may not even exist on
disk, leaving the store contributing no candidate at all.

Iterate over every library-dir ghc-pkg reports and glob for the actual
.so in each, so all present builds become candidates and the chooser
can disambiguate.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>